The family of a mentally ill man who died in police custody has accused investigators of failing to conduct a fair inquiry into his death.

Sean Rigg died after being arrested in Balham, but four months later no officers involved have been interviewed and the cause of death is unknown.

His family, who live in Tooting, say the Independent Police Complaints Commission (IPCC) has not been open with them over key evidence.

Samantha Rigg-David, 38, sister of the dead man, said: “My brother is someone with an illness. He wasn’t afforded the respect or care that a person like this needs.

“He has ended up dead and now they’re not giving us, the family, the justice we deserve. It’s as if they’re trying to cover it up.”

Mr Rigg, 40, was physically fit and a talented musician, but suffered from schizophrenia and lived in a special hostel.

She claims on August 21 he had a breakdown and hostel staff called 999 six times asking police to take him to hospital, but they refused.

He later left the hostel in a disturbed state, and was arrested after a passer-by noticed his strange behavior and alerted police, according to Mrs Rigg-David.

Mr Rigg arrived Brixton police station in a van at 7.30pm but collapsed and was was pronounced dead in hospital two hours later.

An inquest has not yet taken place, but Mrs Rigg-David says a pathologist commissioned by the family pointed to a restraint-related death.

The family claims they were originally told the only injury was a scratch to the cheek but, after arguing for over two hours to see the body, they found a round red mark on his forehead.

Ms Rigg-David said: “It was a red blunt wound. We thought it had been done with a round instrument. It looked like he had been hit.

“We will not stop until we get to the bottom of this.”

They are now conducting their own investigation, and are suspicious of police claims that CCTV cameras in crucial spots were either non-existant or not working.

Tooting MP Sadiq Khan is meeting the IPCC this week to discuss his concerns about the case.

When contacted, Brixton police and the IPCC said they were committed to a thorough and impartial investigation and that the family were being informed on progress as far as possible.

The IPCC added a post-mortem by a Home Office pathologist showed no signs of death-causing injury.

A Ministry of Justice spokesperson said: “Coroners offices always endeavour to deal with bereaved families as sensitively as possible.”